Forming tool for forming the undulating heat exchanger surfaces of a heat exchanger via cold bending of a sheet and method for the realization of the forming profile of such a tool

ABSTRACT

This invention is a device for forming heat exchange elements with corrugated heat exchange surfaces, more particularly inserts, made of a sheet in a formable material, such as metal, between two surfaces, each thus presenting a corrugated profile.  
     This device is of the type comprising at least two plates whose opposing faces present the said corrugated profiles and which are offset from each other so as to define between them a space to take the sheet to be formed ( 2 ). The device is distinguished by the fact that the profiles (A and B) are configured in such a way that their displacement in the direction of the thickness of the insert is constant along the corrugations in the space between the profiles.  
     The invention can be used for the production of inserts.

[0001] The invention is a device for forming heat exchange elements with corrugated heat exchange surfaces, more particularly inserts, made of a sheet in a formable material, such as metal, between two surfaces, each thus presenting a corrugated profile, of the type comprising at least two plates whose opposing faces present the said corrugated profiles and which are offset from each other so as to define between them a space to take the sheet to be formed, and a method of producing the profiled surfaces of the plates of this device for forming corrugated heat exchange surfaces.

[0002] Devices of this type already exist which have an upper plate and a lower one whose forming surfaces present identical profiles and which can be positioned by a lateral movement of one plate relative to the other.

[0003] The existing device has the drawback illustrated in FIG. 1 that the space for the formed sheet, i.e. the insert, is not constant in the direction of the corrugation. In fact, since profiles A and B are identical, the offset in direction y is obviously constant for all the values of x in a system of coordinates x, y, but the thickness in the angled areas, such as, for example, at point E is less than that at the top areas S of the profiles. As a result, the existing devices do not allow one to obtain the best shape at every point of the heat exchange surfaces and, moreover, cause tears in the places where the space to take them is narrowest.

[0004] The invention presented here aims to propose a forming device of the type mentioned above and a method of production of the forming plates which alleviate the above-mentioned drawbacks.

[0005] In order to achieve this aim, the invented device is distinguished by the fact that the profiles are configured so that their displacement in the direction of the thickness of the insert is constant along the corrugations in the space between the profiles.

[0006] The production method of the profiles in the invention is distinguished by the fact that it consists in defining the curve which passes through the centre of the sheet formed between the two profiles and establishing as forming profiles those that are obtained by adding a constant distance on both sides of the curve for each point of the latter, in the direction perpendicular to this curve.

[0007] A distinctive feature of the invention is that the constant distance is equal to the sum of the thickness of the insert and of the play or clearance necessary to the forming, divided by two.

[0008] The invention will be better understood, and its other aims, characteristics and advantages will become clearer in the explanatory description below made with reference to the annexed diagrams, given only as an example, illustrating a way of realising the invention and in which:

[0009]FIG. 1 is a diagram of a device with the present state of the technique;

[0010]FIG. 2 illustrates the paired profiles of the two plates used together in the device as in the invention, in order to illustrate the making of these profiles;

[0011]FIG. 3 is a view in perspective of a forming plate;

[0012]FIG. 4 is a simplified view in perspective of a machine for forming heat exchange surfaces, equipped with a device as in the invention;

[0013] FIGS. 5 to 10 illustrate different stages of forming heat exchange surfaces with the aid of the device illustrated in FIG. 4.

[0014] To make it easier to understand the invention, here is a description, before the invention is shown, of the general structure of a machine equipped with a device for forming heat exchange surfaces, with reference to FIGS. 3 to 10.

[0015]FIG. 4 shows a forming machine 1 with a corrugated strip, hereafter called an insert, obtained by cold-folding a sheet 4 indicated diagrammatically in FIGS. 5 to 10 but which is not visible in FIG. 4. The forming is achieved with the help of an upper forming apparatus 6 and a lower apparatus 7. The upper apparatus 6 and the lower apparatus 7 are each made up of two forming plates and a spacing plate which determines the space between the two forming plates. Thus the upper apparatus 6 comprises the two forming plates 6 a and 6 b and the spacing plate 6 c whereas the lower apparatus 7 comprises the two forming plates 7 a and 7 b and, between these two plates, the spacing plate 7 c. The upper apparatus c is mounted on a vertically adjustable tool holder 10 whereas the lower apparatus is mounted on a lower tool holder 11 which is horizontally adjustable. The upper and lower apparatuses 6 and 7 have strippers, 13 and 14 respectively, which are there to guide and support the sheet 4 during forming.

[0016] As for the sheet in its formed or inserted state, it is folded so as to be made up of a succession of fins A3 and A4, in the direction of the arrow F, which are open alternately towards the top and the bottom, each fin presenting a U-shaped cross-section. On the other hand, in the direction at a right angle to the arrow F, each fm presents a corrugated profile.

[0017] It is easy to understand that the height and spacing of the fins and the geometry of the profile of their lateral surfaces are determined by the dimensions of the plates, the shape of the latter and their positions relative to each other.

[0018] To form the fins and their corrugated surfaces, the sheet in the form of a continuous strip is inserted into the back of the machine shown in FIG. 4, passes between the upper 6 and lower 7 plates, to then be formed by successive alternate folding, and is guided on the supporting housing where the rough cutting of the formed insert (not shown) will take place. The upper and lower strippers 13 and 14 allow the sheet to be guided and to hold it on the lower 7 a and 7 b or upper 6 a and 6 b plates through the progression of the forming cycle. These strippers are only connected to the apparatuses in their horizontal movements.

[0019] A forming cycle can be broken down into six successive stages corresponding to FIGS. 5 to 10.

[0020]FIG. 5 shows the first stage during which the upper apparatus 6 forms the fin A2 which is open towards the top, for the first time, and forms the fin A1, which is open towards the bottom, for the second time. The strippers 13 and 14 guide and support the sheet in the forming process. In the second stage the upper apparatus 6 disengages by moving up and the strippers hold the pressed sheet on the lower apparatus 7. In the third stage, illustrated in FIG. 7, the lower apparatus 7 moves horizontally to the right and thus puts itself in position for the production of the fin A2 for the second time and of fin A3 for the first time. FIG. 8 shows the fourth stage during which the upper apparatus 6 forms the fin A3, which is open towards the bottom, for the first time and forms the fin A2 for the second time, the strippers guiding and supporting the sheet during forming. In the fifth stage, the pressed sheet is supported by the strippers on the upper apparatus 6, which disengages. Finally FIG. 10 illustrates that in the sixth stage the lower apparatus 7 puts itself in position to carry out the forming of the fin A3 for the first time and fin A4 for the second time. At the end of these six stages, the forming cycle starts again at the first stage.

[0021] As was written above, with reference to FIG. 1, the devices used to date have the major drawback that the space to take the sheet is not uniform along the corrugations. The invention proposes a method that allows the production of devices that alleviate the drawback of the irregular thickness along the corrugations.

[0022]FIG. 2 illustrates the method in the invention. This figure shows the paired

[0023] profiles of an upper plate, for example 6 a, and a lower plate 6 b giving between them the corrugation of the insert 2, determined by the profiles of the forming plates, to the plate 4. The thickness of the insert is indicated by the reference ep. One can ascertain on both sides of the insert 2 a play or clearance j/2 whose dimensions are exaggerated in relation to the thickness of the sheet and which is intended to allow for a film of lubricant, amongst other things.

[0024] In general, the method in the invention consists of establishing the curve of the insert in the middle of the latter and then adding in the direction perpendicular to this curve, on both sides of it, a constant distance d which is equal to the sum of the thickness ep of the insert and of the play j needed for the forming, divided by two, i.e. equal to formula: $d = \frac{{e\quad p} + i}{2}$

[0025] By way of an example a description is given below of the method in the invention as applied to a formed sheet with a sinusoidal corrugation. The curve, which will thus be a sinusoidal one, is thus, in Cartesian coordinates, of the type:

γ=a sin(bx)

[0026] To determine the two paired profiles according to FIG. 2, one calculates for each point of the curve two other points situated on the perpendicular to this curve, on both sides of the latter, at the constant distance d indicated above. It is these points that define the two paired profiles.

[0027] More precisely, for an insert with sinusoidal corrugation, so as to determine the Cartesian coordinates of the points for the paired profiles, one calculates the angle of the tangent to each point of the base curve, for example P1, then one adds to the Cartesian coordinates x1, y1 of this point:

[0028] d sin(θ) on the X-axis and d cos(θ+π) on the Y-axis for one of the paired profiles and

[0029] d sin(θ) on the X-axis and d cos(θ+π) on the Y-axis for the second paired profile.

[0030] The Cartesian coordinates xc1, xc2, yc1 and yc2 of these two points established on both sides of the base curve and which are situated on the two profiles required are as follows:

[0031] ti xc1=x1+d sin(θ+π) and yc1=y1+d cos(θ)

xc2=x1+d sin(θ) and yc2=y1+d cos(θ+π)

[0032] The upper and lower apparatuses thus determined are best made in a strong steel alloy (molybdenum cobalt, chrome, tungsten and vanadium) and treated at a very high hardness e.g. 66 HRC. The mathematical definition of the profile allows a manufacturing method on an automatic machine.

[0033] Of course, the invention allows the production of profiles for forming corrugated inserts of any desired shape. It is only necessary to establish, fortunately by mathematics, the central curve of the insert and to define the points of the paired forming profiles according to the method explained above.

[0034] The invention thus allows the forming of sheets of constant thickness, at the same time avoiding the risk of tearing, which is inherent in the method of producing inserts by the existing technique. 

1. Device for forming heat exchange elements with corrugated heat exchange surfaces, more particularly inserts, from a sheet of formable material such as metal, between two surfaces, each one thus presenting a corrugated profile, of the type comprising at least two plates whose opposing faces present the said corrugated forming profiles and which are offset from each other so as to define between them a space to take the sheet to be formed, with the distinction that the profiles (A and B) are configured in such a way that their offset in the direction of the thickness of the insert is constant along the corrugations in the space between the profiles.
 2. Method for making the profiles in claim 1, distinguished by the fact that it consists in defining the curve which passes through the centre of the sheet formed between the two profiles (A and B) and in establishing as forming profiles those obtained by adding, on both sides of the said curve for each point of the latter, a constant distance in the direction perpendicular to this curve.
 3. Method relating to claim 1, distinguished by the fact that the constant distance (d) is equal to the sum of the thickness (ep) of the insert (2) and the play or clearance (j) needed in forming, divided by two. 